Concurrent partnerships speed transmission of HIV through sexual networks much more effectively than does serial monogamy with the same total number of sexual partners. The social and economic environment in which many African Americans live discourages long-term monogamy and promotes concurrent partnerships. Extensive involvement in concurrency may be a key factor in the epidemics of HIV and other sexually transmitted infections (STIs) among African Americans. We propose the following hypotheses: (1) African American men and women are more likely than white men and women to have had heterosexual concurrent partnerships during the preceding 12 months. (2)Involvement in concurrent partnerships is related to lower community sex ratio, education, and marriage rates, and to higher unemployment, poverty and crime rates. These adverse social and economic conditions will largely account for the racial difference in concurrency. We will test these hypotheses through multilevel analyses in the over 12,000 men and women who participated in the 2002 National Survey of Family Growth. We will compare dates of first and last sexual intercourse with each of up to three partners in the past year, to identify concurrent partnerships. Data analyses will examine racial/ethnic differences in the prevalence, characteristics, and extent of involvement in concurrent partnerships among men and women. Stratified and multiple logistic regression analyses will investigate associations with individual-level variables (e.g., sexual history, marital status, and socioeconomic indicators) and, through multilevel analyses, with aspects of the social and economic environment. The study constitutes an important first step in development of future intervention studies and policies to effectively decrease the racial disparity in HIV infection rates. [unreadable] [unreadable] [unreadable]